1. Field of the Invention
The present invention relates to a method for spheroidizing molten iron available for producing ductile cast iron, and a ladle for use in the same method for spheroidizing.
2. Description of the Prior Art
In the case of spheroidizing molten iron to produce ductile cast iron, it is a common practice to use a conventional ladle or a ladle provided with a reaction chamber.
When producing ductile cast iron, in order to change the metallurgical structure of graphite from flakes to nodules, spheroidizing is effected by adding or inserting spheroidizing material into molten metal.
The above-mentioned spheroidizing methods include a set pouring method in which spheroidizing material is preliminarily added into a ladle and then molten metal is poured into the ladle, and a candy method in which a block of spheroidizing material (candy type) is inserted into molten metal within a ladle.
The set pouring method in the prior art is shown in FIG. 17, and the candy method in the prior art is shown in FIG. 18.
In the set pouring method in the prior art illustrated in FIG. 17, a necessary amount of spheroidizing material 2 is preliminarily disposed within a ladle main body 1, and cover material 8 for suppressing the reaction is disposed above the spheroidizing material 2.
Molten metal 4 for producing ductile cast iron within a smelting furnace is poured into the ladle main body 1 and spheroidizing of the molten metal 4 is effected.
In the candy method in the prior art illustrated in FIG. 18, after the molten metal 4 for producing ductile cast iron has been poured into the ladle main body 1 in an amount of about 60%, for example, of the ladle capacity, a cover 8 for preventing the splashing of molten metal and provided with a candy rod 9 having a block of spheroidizing material (candy) 2 is set on the ladle main body 1. Thereafter, spheroidizing of the molten metal 4 is effected by inserting the block of spheroidizing material 2 into the molten metal 4.
In the above-described method for spheroidizing molten metal for producing ductile cast iron in the prior art, a violet flash of light and a large amount of white smoke would be generated, and not only does this greatly deteriorate the environment within a factory, but it also becomes a social problem by generating a public hazard.
In addition, because of an abrupt reaction of the spheroidizing material, due to violent bubbling of the molten metal, spheroidizing of molten metal in the amount of only about 60% of the capacity of the ladle can be effected. Also, the risk of generating a hazard due to splashing of the molten metal is large. Therefore, this method presents safety problems.
A known method for resolving these problems involves handling the entire ladle almost as a sealed pressure vessel during spheroidizing. However, this method has not been put to practical use, because the reliability of this method is very poor and the effect produced thereby is not sufficient.